The present invention relates to a new type of polygonal cutting insert for application in rotary milling tools for machining of metallic workpieces. In particular, the invention relates to a new type of cutting insert with optimized insert geometry so as to be useful in both end mills and milling cutters for flat milling.
Milling inserts are generally manufactured through form pressing and sintering of a powder capable of forming a cutting element. The development is concentrated today on positive cutting edges with positive rake angles since these showed the ability to reduce the cutting forces and the power supply needed in a tooling machine at the same time as undesirable vibrations can be diminished thereby. It is often aimed to provide the tool with a geometry implying a positive axial angle and simultaneously a negative radial angle. In certain cases also a combination of positive axial angle and zero degree radial angle can be used in order to obtain a helical chip that provides best chip transport. The cutting insert is usually clamped with a center locking screw in order to provide the best possibilities for chip transport without problems.
One of drawbacks with existing indexable inserts normally used for end mills has been that they do not entirely avoid problems involving chip entanglement. This problem occurs specifically during the machining of materials that result in long chips. As a solution of this problem, it has been proposed to use a cutting insert, the cutting edges of which are spirally curved. European Document 0 416 901 (corresponding to U.S. Pat. No. 5,078,550) shows and describes such a tool. With such spiral cutting edges the cutting edge can easier come into engagement with the workpiece with an inclined curve of the cutting force up to a maximum value which lies under the value achieved with a straight cutting edge. The tool has in this way obtained a somewhat better stability, but the problem with chip entanglement has remained unresolved when using inserts with a central hole, especially during the machining of long chip producing materials.
In view hereof it is a purpose of the invention to achieve a modified cutting insert of the type described in U.S. Pat. No. 5,078,550, with improved geometrical optimization, implying constant functional edge angle in combination with step clearance along a wave shaped edge line intended to be mounted with large axial inclination in the tool at the same time as the rake face has obtained a more optimized contour.